Elsevier

Applied Soil Ecology

Volume 58, July 2012, Pages 45-55
Applied Soil Ecology

Soil microbial biomass, functional microbial diversity, and nematode community structure as affected by cover crops and compost in an organic vegetable production system

https://doi.org/10.1016/j.apsoil.2012.03.008Get rights and content

Abstract

Soil microorganisms play a crucial role in mineralization and breakdown of complex organic compounds in soil. Microbial populations and functional diversity are greatly influenced by quantity and quality of crop residue and other incorporate organic amendments. This study investigated the effect of cover crops (rye or a mixture of rye-vetch) and compost on soil microflora and microfauna under an organic tomato production system. Each cover crop treatment was used in conjunction with or without compost in a split-plot experimental design. Data on soil respiration, microbial biomass, metabolic quotient, and nematode populations were measured at the end of the growing season. Metabolic characteristics of the soil microbial community were determined using 31 C substrates on Biolog-EcoPlate™. Community level physiological profile (CLPP) was assessed by calculating average well color development (AWCD), richness (S), Shannon–Wiener diversity index (H), and evenness (E). Effect of compost was more pronounced on soil respiration than cover crop treatment. Highest microbial biomass was found in the soils amended with rye and compost (195–210 μg g dry soil−1). Regression analysis between microbial biomass and soil organic matter (SOM) showed strong correlation (R2 value of 0.68–0.56) in two out of the three growing seasons. Calcium, magnesium, and potassium concentrations in soil also positively correlated with microbial biomass. There were significant differences among soils in numbers of plant parasitic, bacterial, and fungal feeding nematodes during the initial years of the study but the differences were not evident later. Shannon–Wiener diversity index was significantly affected by cover crop treatment with rye treatments generally exhibiting higher degree of soil microbial functional diversity. Biolog-EcoPlate™ assay was sensitive to changes in the short-term. Principal component analysis of the Biolog data allowed differentiation of treatments but distribution patterns varied from year to year. We conclude that both rye and rye-vetch mixture can affect the functional diversity of soil microbial community but differences between them are marginal when compared to compost and no-compost treatments. Microbial communities were more responsive to compost applications than cover crop effects.

Highlights

► Cover crops and compost affect soil microbial biomass and functional diversity. ► Rye-vetch mixture significantly increased soil respiration and microbial biomass. ► Nematode population differences leveled off by the end of the final growing season. ► Compost application increased microbial biomass and functional microbial diversity. ► Compost influenced treatment separation in principal component analysis.

Introduction

A high and increasing demand for sustainably produced fruits and vegetables have encouraged growers to transition to sustainable and organic production systems (Klonsky, 2004). Such ecologically sound systems have the potential to address a number of ongoing issues in mainstream agriculture namely pollution due to chemical fertilizers and pesticides, production loses due to pest and disease pressure, soil degradation, loss of soil fertility and productivity. One of the core philosophies of organic production systems is the development of healthy and productive soil that provide essential nutrients for plant growth, supports diverse and active soil biotic communities, and balances the entire farm ecosystem (Insam, 2001, Mäder et al., 2002). Soil biology is directly linked to agricultural sustainability as it is the driving force behind decomposition processes that break down complex organic molecules and substances and convert them to plant available forms (Friedel et al., 2001). Large, stable, and active soil microbial community is an underpinning for sustaining the productivity of soils under sustainable and organic farming systems. To develop such systems growers adopt strategies such as crop rotations, cover cropping, and application of organic amendments (manures and composts) that significantly increase soil organic matter (SOM) and improve soil biology and quality (Bending et al., 2002, Buyer et al., 2010)

Cereal rye (Secale cereale L.) and hairy vetch (Vicia villosa Roth.) (from now on referred to as rye and vetch, respectively) are among the most common cover crops used in regions with temperate climate because of their winter hardiness, the ability to produce considerable biomass, and, in case of vetch, capacity to fix atmospheric nitrogen (Abdul-Baki et al., 1996). When mowed and incorporated these cover crops add SOM, improve soil structure and increase soil biological activity (Carrera et al., 2007, Lundquist et al., 1999). In a three-year study, Buyer et al. (2010) demonstrated that the integration of both rye and vetch cover crop into crop rotations increased soil microbial biomass (SMB) considerably. Along with cover crops, use of compost and manure is considered as an integral component for organic production as it provides essential plant nutrients, adds SOM, and improves soil quality and structure (Russo and Webber, 2007). Application of manure and compost on agricultural lands has been shown to positively increase and enrich soil food web (bacteria, fungi, protozoan and nematode density) and also affect a number of soil characteristics, including SOM, and soil respiration (Carrera et al., 2007, Ferris et al., 2004, Lundquist et al., 1999, Treonis et al., 2010). With increasing number of growers using cover crops and organic amendments in their production systems, it becomes all the more important to better understand the effects of such strategies on soil microorganisms as they are directly involved in organic matter decomposition and nutrient cycling. After soil incorporation, nutrients available in cover crops and organic amendments have to pass through a decomposition pathway which involves a number of soil microorganisms including, bacteria, fungi, and nematodes. Thus, the quality and quantity of plant residues entering the soil can significantly influence soil microorganisms and soil microbial processes (Govaerts et al., 2007). Both crop residue and SOM quality have the potential to increase functional diversity in soil microbial communities (Bending et al., 2002).

Soil contains enormous number of diverse living organisms that influence various ecosystem processes, including formation of organic matter, recycling of nutrients, modification of soil physical and chemical properties, and suppression of pests and diseases (Coleman et al., 1978). Biological characteristics of soil play a vital role in defining soil quality and health. Soil quality is an effective indicator of soil fertility and reflects changes in soil properties which are both inherent and anthropogenic. Soil quality can be estimated and quantified through evaluation of physical, biochemical, or microbial parameters (Glover et al., 2000). A number of soil microbial parameters such as SMB, respiration, metabolic quotient (qCO2), and community profiles have the potential for use as diagnostic indicators of soil quality. Such indicators have been widely used in discerning changes in soil quality and to make comparisons between different soil types and contrasting management systems (Bending et al., 2004, Schloter et al., 2003).

In this study we compared four organic tomato production systems, which differ, based on plant residues and compost inputs. The specific aim of this study was to investigate the impact of cover crop and compost on soil chemical and biological characteristics and tomato yield. Under different cover crop and compost treatments we evaluated parameters such as SMB, nematode community composition, and microbial diversity of aerobic microbial community that rapidly respond to management systems in a short period of time. A simple approach to measure soil microbial functional diversity is to examine the number of different C substrates that are metabolized by the culturable microbial community. This approach of substrate utilization pattern can be obtained using the Biolog-EcoPlate™ system (Garland and Mills, 1991, Zak et al., 1994). The Biolog-EcoPlate™ system assesses the ability of microbial populations toutilize substrates over time and the speed at which the substrates are utilized. The technique generates a community level physiological profile (CLPP) of aerobicmicrobial communities (Garland and Mills, 1991). In our study we hypothesized that: (1) a cover crop mixture of rye-vetch would enhance microbial biomass, and affect nematode counts and microbial functional diversity when compared to a rye only cover crop and (2) application of compost would positively influence the abundance of SMB, improve soil microbial functional diversity, and increase tomato yield.

Section snippets

Field preparation and production techniques

This study was conducted from 2005 to 2009 at the Horticulture Teaching and Research Center (HTRC), Michigan State University, Holt, MI. The soil was a Capac loam with 0–3% slope. Capac loam is a somewhat poorly drained, moderately to moderately slowly permeable soil formed in loamy glacial till on the low parts of moraines and till plains. The soil at the research site was under transition (starting 2005) from a non-organic corn/soybean rotation to an organic tomato production system. Although

Cover crop biomass and tomato yield

Amount of biomass produced by cover crops varied each year. Over all biomass produced in 2007 was lower than 2008 and 2009 (Fig. 1). Differences in biomass between cover crop treatments were largely due to crop type and compost treatments. Rye-vetch-no-compost treatment consistently performed below average in all the years. This is partly due to low seeding rate of rye in rye-vetch treatment, low fertility, and poor establishment of vetch as a result of late planting dates. Rye-compost

Discussion

The objective of this study was to understand changes in below ground biology brought out by two very commonly used organic amendments, cover crops and compost, under an organic production system. We focused on rye and arye-vetch mixture, as they are suitable to temperate climatic regions and a widely accepted cover crop system. During the course of our study the amount of cover crop biomass added to the treatments varied between treatments. Although organic growers generally mix rye with a

Conclusion

Overall our results demonstrate that soil management practices, such as the practice of cover cropping and compost application can enhance soil biological activity. Soil biological properties such as respiration, microbial biomass, nematode population, and microbial functional diversity can be used an indicator of management induced, changes to soil quality. For most soil biological properties evaluated, use of rye or rye-vetch mixture did not lead to major differences; however, the use of

Acknowledgments

We thank Aristarque Djoko, Buck Counts, Pamela Nichol, and the support staff at Horticulture Teaching and Research Center at Michigan State University for their assistance with composting, crop planting, irrigation, and harvesting operations. This work was supported by a grant from the United States Department of Agriculture (USDA Grant no. 2005-51300-02391.

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